U.S. patent application number 14/794712 was filed with the patent office on 2017-01-12 for additive manufacturing of joining preforms.
This patent application is currently assigned to General Electric Company. The applicant listed for this patent is General Electric Company. Invention is credited to Jeffrey Michael Breznak, Andrew Batton Witney.
Application Number | 20170008084 14/794712 |
Document ID | / |
Family ID | 56368846 |
Filed Date | 2017-01-12 |
United States Patent
Application |
20170008084 |
Kind Code |
A1 |
Witney; Andrew Batton ; et
al. |
January 12, 2017 |
ADDITIVE MANUFACTURING OF JOINING PREFORMS
Abstract
A method of fabricating a joining preform includes the step of
printing a self-fluxing joining alloy. Joining includes brazing and
soldering. The self-fluxing joining alloy contains at least one of
phosphorus, boron, fluorine, chlorine, or potassium. Another
printing step prints a non-phosphorous joining alloy. Both printing
steps are performed by an additive manufacturing or 3D printing
process. The printing a self-fluxing joining alloy step may be
repeated until the non-phosphorous joining alloy is substantially
encapsulated by the self-fluxing joining alloy. The self-fluxing
joining alloy may be a BCuP alloy, a CuP alloy, a CuSnP alloy, a
CuSnNiP alloy or a CuAgP alloy. The non-phosphorous joining alloy
may be a BAg alloy, a BNi alloy or a BAu alloy.
Inventors: |
Witney; Andrew Batton;
(Schenectady, NY) ; Breznak; Jeffrey Michael;
(Waterford, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
General Electric Company |
Schenectady |
NY |
US |
|
|
Assignee: |
General Electric Company
|
Family ID: |
56368846 |
Appl. No.: |
14/794712 |
Filed: |
July 8, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B23K 35/3033 20130101;
B23K 35/0244 20130101; B23K 35/3611 20130101; B23K 35/262 20130101;
B22F 5/10 20130101; B23K 35/0238 20130101; B23K 35/0222 20130101;
B23K 35/3013 20130101; B23K 35/362 20130101; B23K 35/3605 20130101;
B23K 26/342 20151001; B33Y 10/00 20141201; B22F 2999/00 20130101;
B23K 35/3603 20130101; B23K 26/354 20151001; B23K 35/3006 20130101;
B22F 3/1055 20130101; B22F 5/009 20130101; B22F 7/06 20130101; B23K
35/302 20130101; B23K 35/3606 20130101; Y02P 10/25 20151101; B33Y
70/00 20141201; B22F 2999/00 20130101; B22F 2207/01 20130101 |
International
Class: |
B22F 3/105 20060101
B22F003/105; B23K 35/26 20060101 B23K035/26; B23K 26/00 20060101
B23K026/00; B23K 35/36 20060101 B23K035/36; B23K 35/362 20060101
B23K035/362; B23K 26/342 20060101 B23K026/342; B23K 35/02 20060101
B23K035/02; B23K 35/30 20060101 B23K035/30 |
Claims
1. A method of fabricating a joining preform, the method
comprising: printing a self-fluxing joining alloy, the self-fluxing
joining alloy containing at least one of phosphorus, boron,
fluorine, chlorine, or potassium; printing a non-phosphorous
joining alloy; repeating the printing a self-fluxing joining alloy
step until the non-phosphorous joining alloy is substantially
encapsulated by the self-fluxing joining alloy; and wherein both
printing steps are performed by an additive manufacturing
process.
2. The method of claim 1, wherein the self-fluxing joining alloy is
at least one of: a BCuP alloy, a CuP alloy, a CuSnP alloy, a
CuSnNiP alloy or a CuAgP alloy.
3. The method of claim 1, wherein the non-phosphorous joining alloy
is at least one of a BAg alloy, a BNi alloy, a BAu alloy.
4. The method of claim 1, the printing a self-fluxing joining alloy
step further comprising: printing the self-fluxing joining alloy on
a part to be joined.
5. The method of claim 1, wherein the joining preform is formed
into at least one of: a cylinder, a disc, a sheet or a washer.
6. The method of claim 1, wherein the printing a self-fluxing
joining alloy step further comprises: printing multiple layers of
the self-fluxing joining alloy, each of the layers having a
different percentage of phosphorus.
7. The method of claim 6, the multiple layers comprised of a
plurality of inner layers and a plurality of outer layers; and
wherein the outer layers have a different percentage of phosphorus
than the inner layers.
8. The method of claim 6, the multiple layers comprised of a
plurality of inner layers and a plurality of outer layers; and
wherein the outer layers have a different melting point than a
melting point of the inner layers.
9. A method of fabricating a joining preform, the method
comprising: printing a non-phosphorous joining alloy; printing a
self-fluxing joining alloy on the non-phosphorous joining alloy,
the self-fluxing joining alloy containing at least one of
phosphorus, boron, fluorine, chlorine, or potassium; and wherein
both printing steps are performed by an additive manufacturing
process.
10. The method of claim 9, wherein the self-fluxing joining alloy
is at least one of a BCuP alloy, a CuP alloy, a CuSnP alloy, a
CuSnNiP alloy or a CuAgP alloy.
11. The method of claim 10, wherein the non-phosphorous joining
alloy is at least one of a BAg alloy, a BNi alloy, or a BAu
alloy.
12. The method of claim 10, the printing a non-phosphorous joining
alloy step further comprising: printing the non-phosphorous joining
alloy on a part to be joined.
13. The method of claim 10, wherein the joining preform is formed
into at least one of: a cylinder, a disc, a sheet or a washer.
14. The method of claim 10, wherein the printing a self-fluxing
joining alloy step further comprises: printing multiple layers of
the self-fluxing joining alloy, each of the layers having a
different percentage of phosphorus.
15. The method of claim 14, the multiple layers comprised of a
plurality of inner layers and a plurality of outer layers; and
wherein the outer layers have a higher percentage of phosphorus
than the inner layers.
16. The method of claim 14, the multiple layers comprised of a
plurality of inner layers and a plurality of outer layers; and
wherein the outer layers have a different melting point than a
melting point of the inner layers.
17. A method of fabricating a brazing preform, the method
comprising: printing a self-fluxing braze alloy, the self-fluxing
braze alloy containing phosphorus, the self-fluxing braze alloy is
at least one of a BCuP alloy, a CuP alloy, a CuSnP alloy, a CuSnNiP
alloy or a CuAgP alloy; printing a non-phosphorous braze alloy, the
non-phosphorous braze alloy is a BAg alloy; repeating the printing
a self-fluxing braze alloy step until the non-phosphorous braze
alloy is substantially encapsulated by the self-fluxing braze
alloy; and wherein both printing steps are performed by an additive
manufacturing process, and the brazing preform is formed into at
least one of a cylinder, a disc, a sheet or a washer.
18. The method of claim 17, the printing a self-fluxing braze alloy
step further comprising: printing the self-fluxing braze alloy on a
part to be brazed.
19. The method of claim 17, wherein the printing a self-fluxing
braze alloy step further comprises: printing multiple layers of the
self-fluxing braze alloy, each of the layers having a different
percentage of phosphorus.
20. The method of claim 19, the multiple layers comprised of a
plurality of inner layers and a plurality of outer layers, the
outer layers having a different percentage of phosphorus than the
inner layers, and the outer layers having a different melting point
than the inner layers.
Description
BACKGROUND OF THE INVENTION
[0001] The invention described herein relates generally to joining
More specifically, the invention relates to a method of printing
soldering and brazing preforms using additive manufacturing.
[0002] The stator windings in large generators may be water-cooled.
The armature windings comprise an arrangement of half coils or
stator bars (collectively referred to as "stator bars" or "bars")
connected at each end through copper or stainless steel fittings
and water-cooled connections to form continuous hydraulic winding
circuits. Water-cooled armature winding bars are comprised of a
plurality of small rectangular solid and hollow copper strands
arranged to form a bar. The rectangular copper strands are
generally arranged in rectangular bundles. The hollow strands each
have an internal duct for conducting coolant through the bar. The
ends of the strands are each brazed to a respective hydraulic
header clip. The hydraulic header clip serves as both an electrical
and a cooling flow connection for the armature winding bar.
[0003] The hydraulic header clip is a hollow connector that
includes an enclosed chamber for ingress or egress of a cooling
liquid, typically deionized water. At one open end, the clip
encloses the ends of the copper strands of the armature winding
bar. A braze alloy bonds the end sections of the strands to each
other and to the hydraulic header clip. The braze joints between
adjacent strand ends and between the strand ends and the clip
should retain hydraulic and electrical integrity for the expected
lifetime of the winding. A typical life time of a winding is on the
order of tens of years.
[0004] Internal surfaces of the brazed joints between the clip and
the ends of the strands are constantly exposed to the deionized,
oxygenated water flowing through the clip and the hollow strands.
In addition, many other liquid filled conduits incorporate brazed
joints exposed to water, such as phase leads, series loops,
connection rings, bushings, as well as the many fittings needed to
connect these conduits. The exposure of the brazed surfaces to the
coolant/water can result in corrosion of conduits. Certain
conditions promote crevice corrosion in the braze joints, such as:
phosphorus, corrosive flux residues, copper, suitable corrosion
initiation sites and water.
[0005] The corrosion process can initiate if the braze joint
surfaces contain surface crevices, pinholes, or porosity at or near
the surface of the joint and the critical water chemistry
conditions that support corrosion. The corrosion process can
progress through the braze joints especially when critical crevice
geometry and water chemistry conditions exist. Porosity within the
braze joints can accelerate corrosion. If allowed to progress
through a joint, corrosion will eventually result in a water leak
through the entire effective braze joint length and compromise the
hydraulic integrity of the liquid filled conduits. Accordingly,
there is a need for a corrosion-resistant brazed joint. The
benefits of a corrosion-resistant brazed joint are expected to
include improved generator availability and generator
reliability.
[0006] Additive manufacturing processes, for example, may generally
involve the buildup of one or more materials to make a net or near
net shape object, in contrast to subtractive manufacturing methods.
Though "additive manufacturing" is an industry standard term (ASTM
F2792), additive manufacturing encompasses various manufacturing
and prototyping techniques known under a variety of names,
including freeform fabrication, 3D printing, rapid
prototyping/tooling, etc. Additive manufacturing techniques are
capable of fabricating complex components from a wide variety of
materials. Generally, a freestanding object can be fabricated from
a computer aided design (CAD) model. One exemplary additive
manufacturing process uses an energy beam, for example, an electron
beam or electromagnetic radiation such as a laser beam, to fuse
(e.g., sinter or melt) a powder material, creating a solid
three-dimensional object in which particles of the powder material
are bonded together. Different material systems, for example,
engineering plastics, thermoplastic elastomers, metals, and
ceramics may be used. Laser sintering or melting is one exemplary
additive manufacturing process for rapid fabrication of functional
prototypes and tools.
[0007] Laser sintering can refer to producing three-dimensional
(3D) objects by using a laser beam to sinter or melt a fine powder.
Specifically, sintering can entail agglomerating particles of a
powder at a temperature below the melting point of the powder
material, whereas melting can entail fully melting particles of a
powder to form a solid homogeneous mass. The physical processes
associated with laser sintering or laser melting include heat
transfer to a powder material and then either sintering or melting
the powder material. Although the laser sintering and melting
processes can be applied to a broad range of powder materials, the
scientific and technical aspects of the production route, for
example, sintering or melting rate, and the effects of processing
parameters on the microstructural evolution during the layer
manufacturing process can lead to a variety of production
considerations. For example, this method of fabrication may be
accompanied by multiple modes of heat, mass and momentum transfer,
and chemical reactions.
[0008] Laser sintering/melting techniques can specifically entail
projecting a laser beam onto a controlled amount of powder material
(e.g., a powder metal material) on a substrate (e.g., build plate)
so as to form a layer of fused particles or molten material
thereon. By moving the laser beam relative to the substrate along a
predetermined path, often referred to as a scan pattern, the layer
can be defined in two dimensions on the substrate (e.g., the "x"
and "y" directions), the height or thickness of the layer (e.g.,
the "z" direction) being determined in part by the laser beam and
powder material parameters. Scan patterns can comprise parallel
scan lines, also referred to as scan vectors or hatch lines, and
the distance between two adjacent scan lines may be referred to as
hatch spacing, which may be less than the diameter of the laser
beam or melt pool so as to achieve sufficient overlap to ensure
complete sintering or melting of the powder material. Repeating the
movement of the laser along all or part of a scan pattern may
facilitate further layers of material to be deposited and then
sintered or melted, thereby fabricating a three-dimensional
object.
[0009] For example, laser sintering and melting techniques can
include using continuous wave (CW) lasers, such as Nd: YAG lasers
operating at or about 1064 nm. Such embodiments may facilitate
relatively high material deposition rates particularly suited for
repair applications or where a subsequent machining operation is
acceptable in order to achieve a finished object. Other laser
sintering and melting techniques may alternatively or additionally
be utilized such as, for example, pulsed lasers, different types of
lasers, different power/wavelength parameters, different powder
materials or various scan patterns to facilitate the production of
one or more three-dimensional objects.
BRIEF DESCRIPTION OF THE INVENTION
[0010] In an aspect of the present invention, a method of
fabricating a joining, brazing or soldering preform includes a
printing step that prints a self-fluxing joining alloy. The
self-fluxing joining, brazing or soldering alloy contains at least
one of phosphorus, boron, fluorine, chlorine, or potassium. Another
printing step prints a non-phosphorous joining alloy. A repeating
step repeats the printing a self-fluxing joining alloy step until
the non-phosphorous joining alloy is substantially encapsulated by
the self-fluxing joining alloy. Both printing steps are performed
by an additive manufacturing process.
[0011] In another aspect of the present invention, a method of
fabricating a joining preform includes a printing step that prints
a non-phosphorous joining alloy. Another printing step prints a
self-fluxing joining alloy on the non-phosphorous joining alloy.
The self-fluxing joining alloy contains at least one of phosphorus,
boron, fluorine, chlorine, or potassium. Both printing steps are
performed by an additive manufacturing process.
[0012] In yet another aspect of the present invention, a method of
fabricating a brazing preform includes a printing step that prints
a self-fluxing braze alloy. The self-fluxing braze alloy contains
phosphorus. As examples, the self-fluxing braze alloy is at least
one of a BCuP alloy, a CuP alloy, a CuSnP alloy, a CuSnNiP alloy or
a CuAgP alloy. Another printing step prints a non-phosphorous braze
alloy which is a is a BAg alloy. A repeating step repeats the
printing a self-fluxing braze alloy step until the non-phosphorous
braze alloy is substantially encapsulated by the self-fluxing braze
alloy. Both printing steps are performed by an additive
manufacturing process, and the brazing preform is formed into at
least one of a cylinder, a disc, a sheet or a washer. The method
may be used to print the self-fluxing braze alloy on a part to be
brazed. The printing a self-fluxing braze alloy step may be used to
print multiple layers of the self-fluxing braze alloy, where each
of the multiple layers has a different percentage of phosphorus.
The multiple layers may have a plurality of inner layers and a
plurality of outer layers, and the outer layers have a different
percentage of phosphorus than the inner layers, and the outer
layers have a different melting point than the inner layers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 illustrates a flowchart of an additive manufacturing
method for manufacturing brazing preforms for turbine,
turbomachinery or dynamoelectric machine components, according to
an aspect of the present invention.
[0014] FIG. 2 illustrates a brazing preform fabricated by the
additive manufacturing method of FIG. 1, according to an aspect of
the present invention.
[0015] FIG. 3 illustrates a cross-sectional view of the brazing
preform of FIG. 2 along sectional line 3-3, according to an aspect
of the present invention.
[0016] FIG. 4 illustrates a cross-sectional view of the brazing
preform of FIG. 2 along sectional line 4-4 of FIG. 3, according to
an aspect of the present invention.
[0017] FIG. 5 illustrates a cross-sectional view of a brazing
preform, according to an aspect of the present invention.
[0018] FIG. 6 illustrates a perspective view of a brazing preform
printed on a part to be brazed, according to an aspect of the
present invention.
[0019] FIG. 7 is a cross-sectional view of the part and brazing
preform along sectional line 7-7 as shown in FIG. 6, according to
an aspect of the present invention.
[0020] FIG. 8 is a perspective view of a brazing preform in the
form of a sheet, according to an aspect of the present
invention
[0021] FIG. 9 is a perspective view of a brazing preform in the
form of a disc.
DETAILED DESCRIPTION OF THE INVENTION
[0022] One or more specific aspects of the present invention will
be described below. In an effort to provide a concise description
of these aspects, all features of an actual implementation may not
be described in the specification. It should be appreciated that in
the development of any such actual implementation, as in any
engineering project, numerous implementation-specific decisions
must be made to achieve the developers' specific goals, such as
compliance with machine-related, system-related and
business-related constraints, which may vary from one
implementation to another. Moreover, it should be appreciated that
such a development effort might be complex and time consuming, but
would nevertheless be a routine undertaking of planning,
fabrication, and manufacture for those of ordinary skill having the
benefit of this disclosure.
[0023] When introducing elements of various aspects of the present
invention, the articles "a", "an", and "the" are intended to mean
that there are one or more of the elements. The terms "comprising,"
"including," and "having" are intended to be inclusive and mean
that there may be additional elements other than the listed
elements. Any examples of operating parameters, materials and/or
environmental conditions are not exclusive of other
parameters/materials/conditions of the disclosed embodiments.
Additionally, it should be understood that references to "one
embodiment", "one aspect" or "an embodiment" or "an aspect" of the
present invention are not intended to be interpreted as excluding
the existence of additional embodiments or aspects that also
incorporate the recited features.
[0024] Referring now to FIG. 1, an additive manufacturing method
100 is illustrated for manufacturing joining preforms for turbine,
turbomachinery or dynamoelectric machine components as disclosed
herein. The term "joining" includes, but is not limited to brazing
and soldering. Brazing is a group of joining processes that produce
coalescence of materials by heating them to the brazing temperature
and by using a filler metal (solder) having a liquidus above
840.degree. F. (450.degree. C.), and below the solidus of the base
metals. Soldering has the same definition as brazing except for the
fact that the filler metal used has a liquidus below 840.degree. F.
(450.degree. C.) and below the solidus of the base metals. The
invention described herein may be applied to joining, brazing and
soldering.
[0025] The additive manufacturing method 100 generally comprises
iteratively fusing together a plurality of layers of additive
material by printing self-fluxing braze (or joining) alloy layers
and non-phosphorous braze (or joining) alloy layers to form a
brazing (or joining) preform. In some embodiments, the
brazing/joining preform may be built/printed directly on the
turbine, turbomachinery or dynamoelectric machine components.
[0026] As one example, the additive manufacturing method 100
comprises a first printing step 110 that prints a self-fluxing
braze/joining alloy. The self-fluxing braze/joining alloy contains
phosphorus, and the phosphorus functions as a flux. The phosphorus
helps during brazing by keeping oxygen from interfering when the
braze/joining alloy initially melts and flows. However, when
phosphorus is trapped in a solidified joint it may be a problem
because the phosphorus increases the susceptibility of a joint to
aqueous corrosion. With this in mind, the less phosphorus that can
be used the better, in that the opportunity for corrosion is
reduced as the amount of phosphorus is reduced. As used herein,
"printing", "iteratively fusing together a plurality of layers of
additive material" or "additive manufacturing" refers to any
process which results in a three-dimensional object and includes a
step of sequentially forming the shape of the object one layer at a
time. A second printing step 120 prints a non-phosphorous
braze/joining alloy on the self-fluxing braze/joining alloy. Steps
110 and 120 may be repeated (step 130) until the non-phosphorous
braze/joining alloy is substantially encapsulated by the
self-fluxing braze/joining alloy or until the desired
brazing/joining preform is obtained. For example, if the
brazing/joining preform requires another layer, than the additive
manufacturing method 100 repeats step 110 and/or step 120. If the
brazing/joining preform does not require another layer, than the
additive manufacturing method 100 can conclude or optionally
advance to a joining process. Both the printing steps 110 and 120
are performed by an additive manufacturing process.
[0027] Additive manufacturing processes include, but are not
limited to, powder bed additive manufacturing and powder fed
additive manufacturing processes such as by using lasers or
electron beams for iteratively fusing together the powder material.
Additive manufacturing processes can include, for example, three
dimensional printing, laser engineering net shaping (LENS), direct
metal laser sintering (DMLS), direct metal laser melting (DMLM),
selective laser sintering (SLS), plasma transferred arc, freeform
fabrication (FFF), and the like. One exemplary type of additive
manufacturing process uses a laser beam to fuse (e.g., sinter or
melt) a powder material (e.g., using a powder bed process).
Additive manufacturing processes can employ powder materials or
wire as a raw material. Moreover additive manufacturing processes
can generally relate to a rapid way to manufacture an object
(article, component, part, product, etc.) where a plurality of thin
unit layers are sequentially formed to produce the object. For
example, layers of a powder material may be provided (e.g., laid
down) and irradiated with an energy beam (e.g., laser beam) so that
the particles of the powder material within each layer are
sequentially fused (e.g., sintered or melted) to solidify the
layer.
[0028] The additive material fused together can comprise a variety
of different potential materials that can depend on, for example,
the type of additive manufacturing method and/or the specific
application for the brazing preform. For example, the additive
material can comprise any material that may be fused (e.g.,
sintered) by a laser beam or other energy source. In some
embodiments, the additive material can comprise a powder metal.
Such powder metals can include, by non-limiting example,
cobalt-chrome alloys, copper alloys, nickel alloys, tin alloys,
silver alloys, aluminum and its alloys, titanium and its alloys,
nickel and its alloys, stainless steels, tantalum, niobium or
combinations thereof.
[0029] FIG. 2 illustrates a brazing/joining preform 200 fabricated
by an additive manufacturing process, according to an aspect of the
present invention. The brazing preform 200 is in the form of a
cylinder or a washer, and includes an outer self-fluxing
braze/joining alloy layer 210 and an inner non-phosphorous
braze/joining alloy layer 220. The inner non-phosphorous braze
alloy layer 220 may be substantially or totally encapsulated by the
self-fluxing braze alloy layer 210. As examples only, the
self-fluxing braze alloy 210 may be comprised of a BCuP alloy, a
CuP alloy, a CuSnP alloy, a CuSnNiP alloy, a CuAgP alloy,
phosphorus, boron, fluorine, chlorine, potassium or any other
suitable self-fluxing braze/joining material or alloy. As a further
example, the non-phosphorous braze alloy 220 may be a BAg alloy,
such as BAg-8, BAg-18 or BAg-24, a BNi alloy, a BAu alloy, or any
other suitable non-phosphorous braze/joining alloy. The BAg-18
alloy is comprised of silver (Ag), copper (Cu) and tin (Sn), and
has a melting point of at about 1,115.degree. F., has a liquidus
temperature of about 1,325.degree. F., and is typically brazed at
temperatures above 1,325.degree. F. A Bag-24 alloy may also be used
as a non-phosphorous braze alloy, and is comprised of silver (Ag),
copper (Cu), zinc (Zn) and nickel (Ni), and has a melting point of
about 1,220.degree. F. and a liquidus temperature of about
1,305.degree. F.
[0030] FIG. 3 illustrates a cross-sectional view of the
brazing/joining preform 200 along sectional line 3-3 of FIG. 2. The
non-phosphorous braze alloy 220 is located in the center of the
brazing preform 200. The self-fluxing braze alloy 210 surrounds and
may substantially encapsulate the non-phosphorous braze alloy 220.
FIG. 4 illustrates a cross-sectional view of the brazing preform
200 along sectional line 4-4 of FIG. 3. It can be seen that the
non-phosphorous braze alloy 220 is surrounded by the self-fluxing
braze alloy 210, and this exposes the phosphorus containing
self-fluxing braze alloy 210 to all exterior surfaces of the
brazing preform 200.
[0031] FIG. 5 illustrates a cross-sectional view of a
brazing/joining preform 500, similar to the view of FIG. 4. The
brazing preform 500 has a central portion comprised of a
non-phosphorous braze alloy 220, which is similar to that shown in
FIGS. 1-4. However, the self-fluxing braze alloy is printed in
multiple layers 510, 512, 514, 516. Each of the layers 510, 512,
514, 516 may have a different percentage of phosphorus or other
constituent elements, and each layer may also have a different
melting point. As one example only, self-fluxing braze alloy layer
510, the outermost layer, may be comprised of BCuP-5, which is 15%
silver (Ag), 80% copper (Cu) and 5% phosphorus (P). The next layer
512 may be a BCuP layer that has only 3% phosphorus, followed by
layer 514 that is a BCuP layer that has only 2% phosphorus and
finally layer 516 is a BCuP layer that has only 1% phosphorus. In
this example, the outer layers have a higher percentage of
phosphorus than the inner layers. The layers 510, 512, 514, 516 may
gradually or drastically increase or decrease the percentage of
phosphorus as they progress inward towards the non-phosphorous
braze alloy 220. This configuration puts phosphorus only where it
is needed, on the exterior portions that will come in contact with
oxygen. The overall braze preform 500 has reduced levels of
phosphorus and the potential for future joint corrosion is greatly
reduced. As another example, layer 510 may be the only layer that
contains phosphorus. Alternatively, the outer layers may have a
lower percentage of phosphorus than the inner layers. The
percentage change of phosphorus may also linearly or exponentially
change across the various layers.
[0032] The self-fluxing braze alloy layers 510, 512, 514, 516 may
have different melting points as well. For example, layer 510 may
have a melting point of at about 1,190.degree. F., and a liquidus
temperature of about 1,300.degree. F., layer 512 may have a melting
point of at about 1,180.degree. F., and a liquidus temperature of
about 1,290.degree. F., layer 514 may have a melting point of at
about 1,170.degree. F., and a liquidus temperature of about
1,280.degree. F., and layer 516 may have a melting point of at
about 1,160.degree. F., and a liquidus temperature of about
1,270.degree. F. In this example the outer layers (510, 512) have a
higher melting point than the melting point of the inner layers
(514, 516). The layers 510, 512, 514, 516 may be configured to have
increasing or decreasing melting points, and more or less that four
layers can be employed, as desired in the specific application.
[0033] FIG. 6 illustrates a perspective view of a brazing preform
200 printed on a part 600 to be brazed/joined, according to an
aspect of the present invention. The part 600 may be a pipe or
fitting and the brazing preform 200 is printed, layer-by-layer, on
the part 600. The part 600 may be any part or component of a
turbomachine or dynamoelectric machine that needs to be brazed.
FIG. 7 is a cross-sectional view along sectional line 7-7, as shown
in FIG. 6. The braze preform 200 has an inner self-fluxing braze
alloy layer 210 in contact with the part 600, a middle
non-phosphorous brazing alloy layer 220 and an outer self-fluxing
braze alloy layer 210.
[0034] Upon application of sufficient heat, the three braze alloy
layers 210, 220 and 210 all melt. The phosphorus-bearing layers 210
in contact with the copper part, self-flux during brazing and give
good adhesion to the parts. The phosphorus-free layer 220 in
between dilutes the phosphorus-rich layers 210 to minimize the
residual presence of Cu.sub.3P phase in the joint, which is a
metallurgical phase that can serve as a site for corrosive attack.
The resulting brazed joint provides enhanced corrosion protection
at the point of contact with flowing fluid (e.g., cooling water, or
any cooling medium).
[0035] FIG. 8 is a perspective view of a brazing/joining preform
800 in the form of a sheet. The outer layer is a self-fluxing braze
alloy 210. An inner layer (not shown) may be formed of a
non-phosphorous braze alloy 220. FIG. 9 is a perspective view of a
brazing/joining preform 900 in the form of a disc. The outer layer
is a self-fluxing braze alloy 210. An inner layer (not shown) may
be formed of a non-phosphorous braze alloy 220.
[0036] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to practice the invention, including making and
using any devices or systems and performing any incorporated
methods. The patentable scope of the invention is defined by the
claims, and may include other examples that occur to those skilled
in the art. Such other examples are intended to be within the scope
of the claims if they have structural elements that do not differ
from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from
the literal languages of the claims.
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